Hydraulic torque converters, devices used to change the ratio of torque to speed between the input and output shafts of the converter, revolutionized the automotive and marine propulsion industries by providing hydraulic means to transfer energy from an engine to a drive mechanism, e.g., drive shaft or automatic transmission, while smoothing out engine power pulses. A torque converter, arranged between the engine and the transmission, typically includes three primary components: an impeller, sometimes referred to as a pump, directly connected to the converter's cover and thereby the engine's crankshaft; a turbine, similar in structure to the impeller, however the turbine is connected to the input shaft of the transmission; and, a stator, located between the impeller and turbine, which redirects the flow of hydraulic fluid exiting from the turbine thereby providing additional rotational force to the pump.
FIG. 1 illustrates a general block diagram showing the relationship of the engine 7, torque converter 10, transmission 8, and differential/axle assembly 9 in a typical vehicle. FIG. 2 shows a cross-sectional view of a prior art torque converter, shown secured to an engine of a motor vehicle, while FIG. 3 shows a left view of the torque converter shown in FIG. 2, taken generally along line 3-3 in FIG. 2. FIG. 4 shows a cross-sectional view of the torque converter shown in FIGS. 2 and 3, taken generally along line 4-4 in FIG. 3. FIG. 5 shows a first exploded view of the torque converter shown in FIG. 2, as shown from the perspective of one viewing the exploded torque converter from the left, while FIG. 6 shows a second exploded view of the torque converter shown in FIG. 2, as shown from the perspective of one viewing the exploded torque converter from the right. The following discussion is best understood in view of FIGS. 1 through 6.
As described above, the three main components of torque converter 10 are pump 37, turbine 38, and stator 39. The torque converter becomes a sealed chamber when the pump is welded to cover 11. The cover is connected to flexplate 41 which is, in turn, bolted to crankshaft 42 of engine 7. The cover can be connected to the flexplate using lugs or studs welded to the cover. The welded connection between the pump and cover transmits engine torque to the pump. Therefore, the pump always rotates at engine speed. The function of the pump is to use this rotational motion to propel the fluid radially outward and axially towards the turbine. Therefore, the pump is a centrifugal pump propelling fluid from a small radial inlet to a large radial outlet, increasing the energy in the fluid. Pressure to engage transmission clutches and the torque converter clutch is supplied by an additional pump in the transmission that is driven by the pump hub.
In torque converter 10, a fluid circuit is created by the pump, the turbine, and the stator (sometimes called a reactor). The fluid circuit allows the engine to continue rotating when the vehicle is stopped, and accelerate the vehicle when desired by a driver. The torque converter supplements engine torque through torque ratio, similar to a gear reduction. Torque ratio is the ratio of output torque to input torque. Torque ratio is highest at low or no turbine rotational speed (also called stall). Stall torque ratios are typically within a range of 1.8-2.2. This means that the output torque of the torque converter is 1.8-2.2 times greater than the input torque. Output speed, however, is much lower than input speed, because the turbine is connected to the output and it is not rotating, but the input is rotating at engine speed.
Turbine 38 uses the fluid energy it receives from pump 37 to propel the vehicle. Turbine shell 22 is connected to turbine hub 19. Turbine hub 19 uses a spline connection to transmit turbine torque to transmission input shaft 43. The input shaft is connected to the wheels of the vehicle through gears and shafts in transmission 8 and axle differential 9. The force of the fluid impacting the turbine blades is output from the turbine as torque. Axial thrust bearings 31 support the components from axial forces imparted by the fluid. When output torque is sufficient to overcome the inertia of the vehicle at rest, the vehicle begins to move.
After the fluid energy is converted to torque by the turbine, there is still some energy left in the fluid. The fluid exiting from small radial outlet 44 would ordinarily enter the pump in such a manner as to oppose the rotation of the pump. Stator 39 is used to redirect the fluid to help accelerate the pump, thereby increasing torque ratio. Stator 39 is connected to stator shaft 45 through one-way clutch 46. The stator shaft is connected to transmission housing 47 and does not rotate. One-way clutch 46 prevents stator 39 from rotating at low speed ratios (where the pump is spinning faster than the turbine). Fluid entering stator 39 from turbine outlet 44 is turned by stator blades 48 to enter pump 37 in the direction of rotation.
The blade inlet and exit angles, the pump and turbine shell shapes, and the overall diameter of the torque converter influence its performance. Design parameters include the torque ratio, efficiency, and ability of the torque converter to absorb engine torque without allowing the engine to “run away.” This occurs if the torque converter is too small and the pump can't slow the engine.
At low speed ratios, the torque converter works well to allow the engine to rotate while the vehicle is stationary, and to supplement engine torque for increased performance. At speed ratios less than 1, the torque converter is less than 100% efficient. The torque ratio of the torque converter gradually reduces from a high of about 1.8 to 2.2, to a torque ratio of about 1 as the turbine rotational speed approaches the pump rotational speed. The speed ratio when the torque ratio reaches 1 is called the coupling point. At this point, the fluid entering the stator no longer needs redirected, and the one way clutch in the stator allows it to rotate in the same direction as the pump and turbine. Because the stator is not redirecting the fluid, torque output from the torque converter is the same as torque input. The entire fluid circuit will rotate as a unit.
Peak torque converter efficiency is limited to 92-93% based on losses in the fluid. Therefore torque converter clutch 49 is employed to mechanically connect the torque converter input to the output, improving efficiency to 100%. Clutch piston plate 17 is hydraulically applied when commanded by the transmission controller. Piston plate 17 is sealed to turbine hub 19 at its inner diameter by o-ring 18 and to cover 11 at its outer diameter by friction material ring 51. These seals create a pressure chamber and force piston plate 17 into engagement with cover 11. This mechanical connection bypasses the torque converter fluid circuit.
The mechanical connection of torque converter clutch 49 transmits many more engine torsional fluctuations to the drivetrain. As the drivetrain is basically a spring-mass system, torsional fluctuations from the engine can excite natural frequencies of the system. A damper is employed to shift the drivetrain natural frequencies out of the driving range. The damper includes springs 15 in series with engine 7 and transmission 8 to lower the effective spring rate of the system, thereby lowering the natural frequency.
Torque converter clutch 49 generally comprises four components: piston plate 17, cover plates 12 and 16, springs 15, and flange 13. Cover plates 12 and 16 transmit torque from piston plate 17 to compression springs 15. Cover plate wings 52 are formed around springs 15 for axial retention. Torque from piston plate 17 is transmitted to cover plates 12 and 16 through a riveted connection. Cover plates 12 and 16 impart torque to compression springs 15 by contact with an edge of a spring window. Both cover plates work in combination to support the spring on both sides of the spring center axis. Spring force is transmitted to flange 13 by contact with a flange spring window edge. Sometimes the flange also has a rotational tab or slot which engages a portion of the cover plate to prevent over-compression of the springs during high torque events. Torque from flange 13 is transmitted to turbine hub 19 and into transmission input shaft 43.
Energy absorption can be accomplished through friction, sometimes called hysteresis, if desired. Hysteresis includes friction from windup and unwinding of the damper plates, so it is twice the actual friction torque. The hysteresis package generally consists of diaphragm (or Belleville) spring 14 which is placed between flange 13 and one of cover plates 16 to urge flange 13 into contact with the other cover plate 12. By controlling the amount of force exerted by diaphragm spring 14, the amount of friction torque can also be controlled. Typical hysteresis values are in the range of 10-30 Nm.
Although assembling blades within a torque converter housing, at first glance, may appear trivial, manufacturing constraints and requirements make the task quite difficult. A shell is formed, e.g., typically by stamping, slots are coined into the shell and subsequently blades are positioned within slots in the shell. Traditionally, the blades have been connected to their respective shell by means of welding. It is to be understood that “welding” in this sense is to be broadly construed. “Welding” is intended to include the following:                Direct fusion of the blades to the shell of the turbine by melting and subsequently hardening at their interface;        Connection by means of an intermediate or connecting molten metal as occurs in gas or arc welding using a metal connecting material usually selected from copper, iron and alloys of at least two of iron, copper, tin, zinc, lead, aluminum, silver, cobalt, chromium and nickel, an example of this method is described in U.S. Pat. No. 3,673,659; and,        Connection using plastic material that is usually a cross linked organic plastic such as an epoxy resin, e.g., as described in U.S. Pat. No. 3,817,656.The most common form of welding utilized in constructing torque converters has been brazing.        
It has been suggested that blades might be secured without welding by utilizing mechanical fastening such as tabs on a blade that are inserted into slots or recesses in a turbine shell. Unfortunately, such devices have had serious disadvantages.
A major disadvantage has been that the blade is not held as securely as when welding is used and the blade may thus vibrate to cause noise, part wear and eventual catastrophic failure. Examples of such devices are described in U.S. Pat. Nos. 2,660,957; 3,673,659; 5,794,436; and, 5,893,704.
A further major disadvantage has been that there has been an inability, by such mechanical fastening, to obtain a tight fit of the blade with the turbine shell. This results in significant inefficiency since fluid within the turbine can pass between the blade and the turbine body thus failing to direct the kinetic energy in that fluid to the turbine and thereby the input shaft of the transmission. Examples of such devices are described in U.S. Pat. Nos. 2,660,957; 3,673,659; and, 5,794,436.
Yet another disadvantage is that the mechanical method of attachment may be difficult, complex or time consuming, e.g., rivets or similar connectors are required or the blades and shells are of complex shapes that are difficult or expensive to manufacture and may require complex interlocking arrangements. Examples of such devices are disclosed in U.S. Pat. Nos. 2,660,957; 3,673,659; and, 5,794,436.
U.S. Pat. No. 5,893,704 describes a structure wherein tabs on the blades are described that fit within recesses in the shell of a turbine. An advantage resulting from this structure is that fluid flow between the blades and the shell is restricted thus increasing efficiency. Unfortunately, the increased efficiency is not as great as desired because fluid flow around the blade is only stopped at the location of the tab and fluid can still flow around the vane at other locations because the tab, as a practical matter, cannot be expected to hold the rest of the edge of the blade tightly against the body. This is true at least due to variations in insertable distance of the tab and variations in curvature of the body relative to curvature of the blade. A further serious disadvantage of this structure is that there is no positive holding force applied to the blade since the tab does not pass through the shell of the turbine but merely rests within a depression by friction.
All of the United States Patents described above are incorporated by reference herein as background art.
As can be derived from the variety of devices and methods directed at assembling a torque converter, many means have been contemplated to accomplish the desired end, i.e., retention of a blade within a shell, without the need for expensive welding operations, and thus resulting in lower assembly cost and complexity. Heretofore, tradeoffs between welding techniques and expense for such methods and steps were required. Thus, there has been a long felt need for a torque converter shell having a blade affixed without welding operations, while introducing minimal changes to the overall process of assembly.